Method of producing magnetic material



United States Patent 3,105,782 METHGD (3F PRQDUCWG MAGNETHI MATERIAL John L. Walter, Scotia, N .Y., assignor to General Electric Company, a corporation of New York No Drawing. Filed Get. 10, 1960, Ser- No. 61,377 16 Claims. (Cl. 148-113) are so oriented that the direction of easiest magnetization through the grains coincides with the direction of magnet ization of the material sheet. their greatly enhanced magnetic proper-ties, have been found to reduce the size, weight and cost of transformers, induction regulators, dynamoelectric machines and other electrical apparatus in which substantial quantities of magnetic flux must be linked with magnetic conductors.

Electrical and electronic equipment including magnetic cores as an essential operating part thereof can deliver optimum performance only when the cores are constructed of a soft magnetic material having high saturation, high permeability, low coercive force, low losses, and a high ratio of residual induction to saturation induction. Additionally, since much electronic equipment is often subjected to elevated temperatures, it is desirable that the saturation induction of the core material be retained at as high a value as possible up to as high a temperature as possible.

Alloys of iron and nickel meet some of the foregoing requirements but saturation induction is only about 75 percent of that which can be obtained in silicon-iron alloys and the cost is comparatively high.

in the Frey et a1. U.S. patent, No. 2,112,084, one method proposed for producing sheet with a preferred orientation comprises subjecting sheet iron-silicon material during its final stages of thickness reduction to one or more specially predetermined cycles of strain reduction and annealing to produce a cold worked texture which after recrystallization results in a well-fibered material having large grains. The recrystallized texture produced by this method is defined in the patent as having the 110) [001] orientation which is generally referred to as cube-on-ed ge. This orientation may be described as one in which the unit cube lattices of the oriented grains have a plane containing diagonally-opposite cube edges substantially parallel to the plane of the sheet and a pair of opposite cube faces substantially perpendicular to the rolling direction and to the plane of the sheet. The (110) [001] designation is based in the Miller Crystallographic Index System, a complete discussion of which may be found in Structure of Metals, C. S. Barrett, 2nd edition, 1952, pages 1-25, published by the Macmillan Company. Material having this orientation is anisotropic and has optimum magnetic prop- Such materials, because of erties in the [001] direction parallel to the direction of rolling, the properties transverse to the direction of rolling being inferior.

Preferred oriented sheet materials have been recently developed in which good magnetic properties are indicated transverse to the direction of rolling, as well as parallel there-to. One such method is described in copending application U.S. Serial No. 610,909 of Hibbard and Walter, filed September 20, 1956, and assigned to the same assignee as the present application. The orientation produced by this method is described as one in which a majority of the grains have their body-centered cubic lattices oriented so that four of the cube faces are substantially parallel to the rolling direction, two of these faces being also substantially parallel with the plane of the sheet and the other two being substantially perpendicular to the plane of the sheet, and the remaining two cube faces substantially perpendicular to both the rolling direction and the plane of'the sheet. This orientation is conveniently termed cube texture or defined in terms of Miller indices, (100') [00 1]. i

. The method of the copending application resides in preparing specially cast ingots having an entirely or substantially entirely columnar as-cast grain structure. These castings are produced so that substantially all the metal therein is comprised of elongated columnar grains, the longitudinal axis of each of which is substantially parallel to each other longitudinal grain axis and all of which axes are substantially parallel to a single direction in the ingot. By appropriately hot, warm and cold rolling as-cast slabs of up to about one inch in thickness or slabs of that thickness cut from larger ingots, with particular reference to the direction of the longitudinal 'axes of the columnar grains to the rolling directions and rolling planes, it was found that the cold rolled structure of the sheet material so produced could be caused to recrystalliz'e upon appropriate annealing to produce sheet or strip material having the desired cube texture. More specifically, this reduction procedure involved heating such slabs to a temperature range of from about 700 C. to about 1100" C., reducing the thickness of the so-heated slabs about to 97 percent in a plurality of rolling passes without reheating, annealing, cold reduc ing the annealed material at least 40 percent in thickness by cold rolling and annealing to effect recrystallization'of the said rolled grain structure to produce the cube-textured sheet or strip material. This casting, rolling and heat treatment procedure was found to be effective to produce strong cube texture in polycrystalline body-centered cubic sheet or strip materials composed of at least 92 percent iron and, more specifically, alloys containing up to about 6 percent silicon, up to about 5 percent molybdenum, and up to about 8 percent aluminum, all useful soft magnetic materials, provided particular care was exercised during casting to insure the desired oriented columnar grains required in carrying out the process.

Prior to this invention, silicon-iron alloys have generally been characterized by high coercive force and a low ratio of residualto-saturation induction. Improvement in the magnetic properties has been obtained through development of silicon-iron bodies having cube-,

on-edge, (110) [001], or cube texture, (100) [001], crystalline orientation. The cube-on-edge oriented material has been widely used in high power applications, such as transformers and the like, in thickness of from 12 to 15 desired preferred orientation texture.

mils. It has not previously been possible to use grain oriented silicon-iron alloys in the construction of magnetic cores used in amplifiers or other electrical or electronic equipment operated under low power conditions. This results from the prior inability to produce oriented silicon-iron bodies of sufficient thinness for use in low power applications. It is desirable to use the thinnest material available, commensurate with reasonable magnetic properties, for low power applications because of the lower eddy current losses.

Applicant has now discovered a new method of obtaining preferred grain orientation by making use of a phenomenon connected with grain growth generally referred to as secondary recrystallization. It differs from primary recrystallization (which occurs when annealing cold worked metals) in that it occursafter primary recrystallization has been completed. It is generally accompanied by an abrupt or pronounced increase in size of the recrystallized grain with a majority of the resulting grains having an orientation based on one of the components present prior to grain growth. Further, it is now possible to produce grain oriented bodies sufficiently thin for use in electronic as well as power applications.

Prior to the present invention, neither the occurrence of secondary recrystallization nor the extent to which one orientation will grow at the expense of another during secondary recrystallization could be predicted with any amount of certainty.

A principal object of this invention is to provide a new process for producing magnetic sheet material having a preferred grain orientation.

Another object of this invention is to provide a process in which predictable secondary recrystallization is employed in preparing a magnetic sheet material having a selected grain orientations.

Another object of this invention is to provide a process for producing grain oriented magnetic sheet material in which the type of grain orientation formed can be controlled and reliably reproduced.

Another object of this invention is to provide thin tapes of high purity silicon-iron alloys having improved magnetic properties rendering them suitable for use in low power applications.

An additional object of this invention is to provide magnetic cores comprising high purity silicon-iron thin tapes having improved magnetic properties.

An additional object of this invention is to provide thin tapes of high purity silicon-iron having an A.-C. residualto-saturation induction ratio of not less than about 0.85.

Other objects and advantages of this invention are in part obvious and in part explained by reference to the accompanying specification.

The present inventionmakes possible the attainment of a number of different preferred orientations in a thin strip or sheet, any one of which can be produced in a given material. A preferred orientation or texture can be selected by control of a number of separate factors including composition, working, annealing temperature and time and the particular atmosphere or environment within which the annealing is carried out.

The magnetic alloys of principal interest consist essentially of iron with about 2 percent to 6 percent silicon, preferably about 2.6 percent to 3.4 percent. :It is to be understood that all composition percentages set forth therein are weight percentages. It is preferred, for optimum results, that the combined iron and silicon content be at least about 99.8 percent of the total composition. Impurities and incidental elements should not exceed a total of about 0.2 percent. Concerning nonmetallic impurities such as sulfur, carbon, oxygen and nitrogen, these should not exceed a total of about 0.02 percent and should be maintained as low as is practicable and preferably not exceed the maximum indicated.

4 Element: Maximum, percent S 0.003

C .003 0 .005 N e .001

When producing thin tapes of up to 3 mils thickness, the impurity content of the alloy should preferably not exceed 0.010 weight percent if optimum properties are to be obtained. The content of irnpurities normally present in material of this nature is carbon, 0.001; sulfur, 0.001; oxygen, 0.001; nitrogen, 0.0005; and some minor percentages of other metallic elements which are normally present in iron.

Broadly speaking, to produce a thin sheet in which a majority of the grains have either cube, (100), or cubeon-eclge, (110), crystal planes contained within or oriented parallel to the flat surfaces of the sheet, the sheet must be no more than about 15 mils (0.015 inch) thick and the oxygen content not more than about 0.005 weight percent (50 parts per million). By conforming to these requirements, which are discussed in greater detaillatcr, control of [the oxygen present at the surface of the sheet is effected through composition control and control of the final annealing atmosphere to achieve one of the two If it is desired that the orientation of the grains be such that the cube edges of the unit cubes be aligned in a common direction, in addition to having the (100) and (110) planes aligned, then the alloy must be physically worked by rolling it down to the desired thickness prior to final annealing. If directional alignment of the unit cubes is unnecessary and alignment only of the (100) or (110) planes parallel to the plane of the sheet desired, then working is unnecessary. Thus,

bodies of 15 mils thickness or less could be made by casting or any other acceptable procedure. a

In the usual process, a cast body is first reduced in thickness to form an intermediate sheet metal product having preferably a nominal thickness of about 0.1 inch (for example, 0.05 to 0.25 inch). A substantial portion of the reduction is effected through hot working in substant ially one direction over a temperature range of about 700 C. to 1200 C. The intermediate is thereafter annealed at an elevated temperature, (for example, 700 C. to 1200 C., for a time sutficient to recrystallize the hot worked texture, e.g., about 0.1 to 10 hours, in an atmosphere substantially non-oxidizing to silicon, such as dry hydrogen having a dew point no higher than 40 F.

The annealed product is then cold worked at least 25 percent in substantially the same direction (e.g., over the range of 40 percent to 99.5 percent) using intermediate anneals where required when more than one r duction stage is used to arrive at thicknesses ranging up to about 0.015 inch. The intermediate anneal, which is also carried out under conditions substantially non-oxidizing to silicon (e.g., dry hydrogen having a dew point no higher than 40 F.), may range in temperature from about 700 C. to 1200 C. for a time sufficient to effect recrystallization, such as 0.1 hour to 10 hours.

After the final thickness has been reached, the cold worked material is then subjected to a final anneal at an elevated temperature in a selected environment for a. sufficient time to primarily recrystallize the cold worked material and for an additional time at said or higher temperature to effect smondary recrystallization. Temperatures for the final anneal may range from about 1000 C. to 1350 C. for times ranging up to about 16' metal and its surrounding environment or atmosphere. Under different conditions, the grains whose (110) planes are disposed parallel to the plane of the strip will grow at the expense of the surrounding grains. Specifically, it has been found that the impurity content ofthe material and, more exactly, the oxygen content, will exert a controlling effect on the growth and orientation of the grains if the sheet material being worked is of relatively thin cross-section. The effect results from surface energies which, depending upon the amount of oxygen prescut, will result either in the growth of a cube-on-edge or a cube texture crystal orientation.

A number of tests were conducted in which varying amounts of oxygen were present on the surface of thin strip material, i.e., less than about 0.015 inch in thickness, and from these tests it was found that the surface energy of the (110) plane was lower than the surface energy of the (100) plane, so that in a pure material, i.e., one containing less than about 6 ppm. of oxygen, the material would develop a cube-on-edge crystal orientation. On the other hand, a material containing in excess of -6 ppm. of oxygen would develop cube texture or cube-on-face orientation as a secondary recrystallization texture. It will be readily appreciated that the critical amount of oxygen, which has just been indicated as 6 p.p.m., may in fact vary somewhat from this value. The first problem encountered in determining what the exact critical oxygen amount is is that of determining what percentage has been present in the materials tested. Chemical analysis of metals to determine these very minor percentages of oxygen contents is extremely diflicult and subject to analytical error. Additionally, where sheets of extremely thin crosssectional dimension, for example, on the order of 2 to 3 mils, are being treated, a somewhat higher oxygen content can be present due to the speed with which the ox gen can be removed as compared to the speed with which it can be removed from a body of 13 mils, for example. Thus, in some situations it is possible to use a commercial or mill material of fairly high purity rather than necessarily using a vacuum-melted material to insure that the impurity content is sufficiently low. In instances where a cleansing atmosphere was used which removed oxygen from the body, a cube texture orientation was obtained as the secondary recrystallization texture. Continued heating brought about the development of a tertiary recrystallization cubeon-edge texture.

Generally, the test used to determine the relative energies between the (100) and (110) planes is as follows: Sheet material 0.3 mm. (about 0.012 inch) thick was prepared by a combination of hot rolling and cold rolling operations, starting with a vacuum-melted ingot of iron containing approximately 3 percent silicon. The total impurity content was less than 0.005 weight percent. The samples were electropolished to remove surface imperfections and then annealed in vacuum at pressures below 5 X mm. mercury at 1200 C. for 1 to 3 hours. The times at temperature were sufficiently long to produce large (100) grains by secondary recrystallization but short enough to prevent the samples from being converted entirely to the (110) [001] texture by tertiary recrystallization.

After preparation, the samples were annealed in impure or wet argon containing a small amount of oxygen or water vapor (welding grade, dew point of 70 F.) at atmospheric pressure and a temperature of 1 200 C. Selected samples were given a second anneal either in argon or in vacuum following the first anneal in hydrogen. Boundaries between (100) and (110) grains were found that advanced into the 100) grains in a vacuum anneal, then reversed their direction of migration and advanced into the (110) grains in a subsequent anneal in impure argon. They then reversed back to the initial direction of migration in a final vacuum anneal. In the anneals in argon, but not in the vacuum, the surfaces of the grains were thermally etched. These results are explained on the basis that the impure argon supplied oxygen atoms, or at least caused no removal of oxygen atom-s already present, and that the vacuum anneals removed oxygen. The conclusions reached were:' (a) that under proper conditions, impurity atoms can effect a reversal in the direction of boundary migration; (11) that the surface energy of the grains is less than the surface energy of the (100) grains in the vacuum anneals and the surface energy of the (100) grains is less than the surface energy of the (110) grains in the anneals in impure argon; (c) the effect of the impurity is to reduce the surface energy of the (100) grains more than the surface energy of the (110) grains; and (d) the high density plane, (110), is therefore not always the low energy plane.

Thus, the nature of the texture which has ultimately developed in the material is dependent upon the amount of oxygen which is present at the surface of the body during the final anneal. With this information, it becomes apparent that control of the oxygen content can be achieved in several ways. Specifically, the oxygen content of the starting alloy may be placed at a suitable level such that the desired orientation can be developed with minimum difficulty. That is, if a cube-on-edge texture is desired, then the oxygen content of the material and the atmosphere should be maintained at an acceptably low level, since its removal is necessary before cube-onedge texture will be totally developed. On the other hand, if oube-on-face or cube texture is sought, then the oxygen content at the surface can be supplied either by insuring that an adequate amount of oxygen is present in the initial alloy or by providing the necessary oxygen from the surrounding environment. In any event, the environment used during the final anneal is instrumental in determining the type of texture which is developed within the body.

Assuming an alloy having an excess of oxygen, cube texture can be obtained by adequately hot and cold rolling the body, as previously outlined, and giving the body a final anneal in one of the noble gases such as argon or krypton, either wet or dry, that is, having a dew point higher or lower than 40 F., respectively, or by annealing it in a cleansing environment such as vacuum or hydrogen for a period of time suflicient to develop cube texture but insufficient to permit continuance of crystallization into the tertiary, cube-on-edge form.

Generally, the oxygen content of the cleansing environment used, viz., hydrogen or vacuum, must be low enough to prevent oxidation of silicon at the 1000 C. to 1350 C. final annealing temperatures. If the oxygen content is in excess of this amount, then the metal body is not lowered sufficiently in oxygen content to develop cubeon-edge orientation. Dry hydrogen, that is, hydrogen having a dew point no higher than 40 F., is an acceptable cleansing atmosphere, as already mentioned. Vacuum containing no more than one micron of oxygen is also effective as it is non-oxidizing to silicon under the specified conditions. Obviously, environments containing less oxygen are completely acceptable.

Thus, if one of the noble gases is used, the time of the final anneal is not critical, whereas if a cleansing environment such as dry hydrogen or vacuum is used, the recrystallization must be stopped in the secondary stage. If oube-on-edge texture is desired, of course, the anneal can be continued for a length of time sufficient to permit growth of the (110) grains at the expense of the alreadyformed (100) grains. This continued growth occurs by reason of the mechanism set forth earlier.

Another factor which must be considered in connection with the oxygen content in the metal and in the environment is the amount of silicon present in the initial alloy. If a silicon content on the order of 2 weight percent is used, then a sufficient amount of oxygen is soluble in the alloy to permit ready development on cube texture or cube-on-edge texture by controlling the factors previously set forth. On the other hand, if a relatively high silicon alloy is used, for example, on the order of or 6 weight percent, then the hydrogen or vacuum environments cannot be used as effectively as an oxygen-containing noble gas atmosphere to obtain cube texture, although cube-on-edge texture can readily be obtained with hydrogen, vacuum or a dry, oxygen-free, noble gas atmosphere. This diificulty arises by virtue of the differing diffusion rates of oxygen in the two alloy compositions. That is, oxygen diifuses much more slowly through an alloy containing 5 percent silicon than it does through one containing 2 percent silicon. Added to this feature is the fact that, normally, less oxygen will be present in the higher silicon alloy than in the lower silicon alloy so that the same amount of oxygen is not readily available for difiusion from within the body to the surface to obtain the desired results.

To illustrate the effect of the oxygen content and the effect of the environment used during the texture-development anneal, an alloy was made by vacuum melting high purity electrolytic iron and silicon and casting to form slabs. The total impurity content was on the order of 0.006 percent by weight. The slab was heated to 1100 C. and rolled to 0.5 inch thickness with reheating between passes to keep the temperature at about 1100 C. The material was then rolled at 1000 C. to 0.25 inch in thickness and annealed at 1000 C. for one hour in dry (dew point 70 F.) hydrogen.

Cold rolling to 100 mils, or 0.100 inch, was effected and this was followed by a five-hour anneal at 700 C. in dry hydrogen, which was in turn followed by additional cold rolling to 50 mil thickness. Annealing was effected at 900 C. for one-half hour in dry (dew point 70 F.) hydrogen, the body cold rolled to 25 mils, then heated to 900 C. for one-halt hour in dry hydrogen of 70 F. dew point and finally cold rolled to a thickness of 12 mils. The cold rolled structure at this point was principally (ll1)[l12]. A portion of the material was then rolled to 0.006 inch thickness, or 6 mils. All samples were electropolished prior to the final anneal to remove surface imperfections, since the outer layer normally contains a high oxygen content and might aiiect the properties of the metal so that qualitative control could not be maintained. Other, standard methods of removing the outer layer of impurities may be used or the layer can be left in place, if desired.

Samples of the material were then finally annealed in either dry hydrogen having a dew point no higher than 40 F., vacuum containing no more than one micron of oxygen, or argon having a dew point no higher than 40 F., as set forth below, with one type of material containing approximately 6 to 7 p.p.m. of oxygen prior to the anneal and the second type of material containing approximately 8 to 10 p.p.m. of oxygen prior to final annealing.

The first type of material which contained 6 to 7 ppm. of oxygen was heated for varying time periods in an argon atmosphere containing some oxygen (dew point -70 F.) at 1200 C. Samples were removed after one-half, one, two, four, and eight hours of annealing to determine what sort of crystal orientation was taking place during the annealing. After one-half hour, the sample contained about percent cube-textured grains; after one hour, about percent; after two hours, about 50 percent; after four hours, about 85 percent; and finally, after eight hours, the specimen was about 98 percent cube textured. Thus, the material contained a suificient amount of oxygen in the presence of argon, which was tank argon having a dew point of 70 F. and therefore supplied some oxygen atoms, to cause cube texture orientation to develop and ultimately consume the entire specimen. Similar procedures and processing were followed with the material containing the higher oxygen content, 8 to 10 p.p.m., and this material developed the same structure, except that a slightly longer final annealing time period was required due to some pinning of grain boundaries by oxide particles.

Samples of the same material used in the preceding example were annealed in vacuum at 1200 C. for onehalf, one, two, four and six hours, with the pressure ranging from 0.02 to 0.06 micron. The oxygen content of the material initially containing 6 to 7 p.p.m. was reduced to about 4 p.p.m. in two hours and reduced to about 3 ppm. after six hours. In this case, since the initial oxygen content was sufiiciently high to induce the growth of cube textures, the samples at first began to grow cube grains and it was not until after about two hours of annealing that the cube-on-edge or (110) planes began to predominate and become the dominant and consuming orientation Ultimately, at the completion of the six-hour annealing period, the samples consisted essentially entirely of a cube-on-edge crystal orientation.

By way of comparison, the higher oxygen material, that is, the material having an initial oxygen content of 8 to 10 ppm. oxygen, consisted essentially entirely of cube texture grains after two hours of annealing, and it was not until annealing had been carried out for a much longer period of time that the samples recrystallized from the cubic texture into the cube-on-edge crystalline orientation.

It is felt that the tests outlined above clearly indicate that there is a critical amount of oxygen above which a cube texture orientation occurs and below which a cubeon-edge crystalline orientation occurs when the bodies are annealed in the proper selected environments.

Samples were also annealed in hydrogen having a dew point of 70 F. for the same lengths of time as inthe vacuum and the same growth pattern was followedwith completion of crystalline orientation taking place after three to eight hours of annealing.

Where a cube-texture type orientation is desired in which the [001] direction is oriented 20 to 30 on either side of the rolling direction, the cold work prior to the final anneal in arriving at the desired thickness will generally range from about 70 percent to 99.5 percent, preferably at least about percent. The final annealing temperature will usually range from about 1000 C. to 1350 C. for a time sufiicient to eifect secondary recrystallization, usually up to about eight hours.

In producing a cube texture orientation with the [001] direction of the crystals random with respect to the rollmg direction, the annealed intermediate is cold rolled 70 percent to percent, annealed over the temperature range of about 700 C. to 1200 C. for a time just sufficrent to primarily recrystallize the cold-wonked texture and then further cold reduced about 40 percent to 70 percent to thickness of less than 0.015 inch followed by annealing over the range of about 1000 C. to 1350 C. for a time sufiicient to effect secondary recrystallization, usually eight hours.

Where a .cube texture orientation is desired in which the [001] direction is within 5 or 10 of the rolling direction, the annealed intermediate is subjected to reductions of 25 percent to 70 percent separated by intermedi ate anneals over the temperature range of 700 C. to 1200 C. for a time sufficient to recrystallize the cold worked structure. The reduction stages are repeated until thicknesses of less than about 0.015 inch are obtained, after which the final material is annealed at a temperature of about 1000 C. to 1350 C. for a time sufiicient to effect secondary recrystallization, for example, up to eight hours. Reductions of 50 percent are preferred to obtain [001] directions within 5 of the rolling direction.

In producing cube texture orientation, the cold reduction stages leading up to the final thickness should be conducted over the range of 25 percent to 70 percent.

The annealing of the final product is similar to the above methods except for the particular environment and the annealing time used, as explained hereinbefore.

As illustrative of the various embodiments of the invention, the following examples are given:

EXAMPLE 1 In producing an ingot of the desired purity, electrolytic iron was melted in a vacuum, treated with hydrogen to remove carbon, nitrogen, sulfur and oxygen, and the iron then solidified to remove the hydrogen. The purified iron was remelted and silicon added in the form of an iron-silicon alloy to produce an alloy containing about 3.5 percent silicon. The alloy was cast in a graphite mold to form a slab 1% inches thick, 6 inches wide and 12 inches long. The iron-silicon alloy produced contained 3.31 percent silicon, less than 0.001 percent manganese, less than 0.001 percent aluminum, 0.003 percent sulfur, 0.003 percent carbon, 0.0005 percent oxygen and 0.0005 percent nitrogen.

The slab which had randomly oriented grains was heated to a temperature of about 1100 C. in hydrogen and rolled to one-half inch in 0.05 inch drafts, followed by reheating to temperature after each draft until the one-half inch thickness was reached. The temperature was then reduced to 1000 C. and the working continued until a slab one-quarter inch thick was obtained. The slab was then annealed in dry hydrogen (dew point 70 F.) at 1000 C. for one hour, heated and cooled rapidly, followed by room temperature rolling to an intermediate product of about 0.1 inch thick.

A section of the intermediate was annealed in dry hydrogen at 700 C. for hours using rapid heating and cooling rates. One portion of the section was rolled to 0.012 inch thick (88 percent reduction) and another portion to 0.003 inch thick (97 percent reduction).

The 0.012 inch sheet was subjected to a high temperature heating in dry (dew point 70 F.) hydnogen at 1200 C. for eight hours, the time being sufiicient to effect primary and secondary recrystallization (i.e., the first stage of secondary recrystallization). The crystals formed were one-half to one and one-half centimeters in diameter. A variation of cube texture was obtained in which the (100) planes were within 4 of parallel to the rolling plane and the [001] directions were oriented 20 to 30 on either side of the rolling direction, wherein about half of the crystals had [001] directions to the left and the other half to the right.

Similar results were indicated for the 0.003 inch sheet. This sheet produces secondary crystals if it is preferably rapidly heated to 900 C. to 1000 C. for 15 minutes to one-half hour and then rapidly heated to 1200 C. and held for eight hours. The crystals here are smaller than those of the thicker sheet.

Minimum cold reduction for complete secondary recrystmlization appears to be in the neighborhood of about 90 percent (i.e., rolling 0.1 inch to 0.008 inch). For example, complete secondary recrystallization was obtained with the thin sheet (reduced 97 percent), whereas over 80 percent of completion was obtained for the 0.012 inch sheet (reduced 88 percent). Heating in argon of similar dew point or in a vacuum of 100 microns of mercury gave similar results.

Examination of the rolled material (0.012 inch thick) recrystallized short of secondary recrystallization (by X-ray difiraction, pole figures and magnetic torque tests) revealed that only about 20 percent of the texture was cube-on-face.

The material produced by this embodiment of the invention is ideal for laminations in rotors and stators of motors and generators.

EXAMPLE 2 A section of the 0.1 inch intermediate of Example 1 was similarly annealed at 700 C. for five hours in hydrogen. Two portions of the annealed intermediate were 10 then cold rolled, one to 0.024 inch, the other to. 0.012 inch, a reduction in thickness of 76 percent and 88 percent, respectively. The 0.024 inch material was annealed at 1200 C. for eight hours, while the 0.012 inch material was annealed at 900 C. for five minutes.

Following the foregoing anneal, the material was cold rolled to reductions of approximately 40 percent and 70 percent and electropolished to remove surface imperfections.

The cold rolled materials were subjected to either one of two annealing treatments, (1) the thicker pieces (0.014 inch) being annealed at 1200 C. (at a heating rate of 100 C. per hour) and held at temperature for eight hours to effect secondary recrystallization, and (2) the thinner pieces (0.007 inch and 0.004 inch) being annealed by heating rapidly to 900 C. for 15 minutes and then rapidly heated to 1200 C. and held for eight hours at temperature in hydrogen of -70 F. dew point.

Size Size After Amount Heat Specimen N0. Before Rolling, Cold Treat- Rolling, inches Work, ment inches percent 0. 024 0. 014 about; 40 1 .024 .007 about 70-.- 2 .012 .004 about 70.-. 2

During heat treatment, samples were removed after completion of primary recrystallization and the orientationv determined by optically examining etch pits. This examination revealed that 5 to 10 percent of the texture in all of the sample specimens was cube-on-face, there being a weak indication of cube-on-edge.

The remaining specimens were then examined after completion of secondary recrystallization. Substantially all of them had a large grain size in which most of the grains had (100) planes within 4 parallel to the rolling plane but with the [001] directions randomly distributed with respect to the rolling direction. Materials with this type of orientation are suitable as elements in rotating electrical equipment.

EXAMPLE 3 Tempeature, Time (hrs) omhmx In all specimens, about 5 percent to 10 percent of the texture was cube-on-face after primary recrystallization, whereas after completion of secondary recrystallization, the (100) planes of the majority of the grains were Within about 4 parallel to the rolling plane while the [001] directions were within 15 of the rolling direction. In the 0.012 inch material, 65 percent of the grains had [001] directions within 15 of the rolling direction. In the 0.006 inch material, percent of the grains were aligned within 10 of the rolling, better alignment being obtained with even thinner materials.

It is apparent from the results of Examples 1 to 3 that several useful textures are possible by means of slight variations in processing in the production of high purity sheet of thicknesses ranging from about 0.0005 inch to 0.015 inch, and preferably from about 0.0005 inch to 0.006 inch. These textures may be deemed to be variations of the cube texture in that they are characterized generally by a substantially cube-on-face type of orientation (the (001) planes being within 4 or 5 of the horizontal or rolling plane), the [001] directions being within and possibly within 5 of the rolling direction in one case, or within or 30 .of the rolling direction in another, or, in still another case, being randomly oriented with respect to the rolling direction. For the purpose of this invention, these variations in preferred orientation are referred to generically as cube-on-face and include the ideal cube texture as the desired product.

'In situations where the cube-on-edge type of orientation is desired, similar processing procedures may be employed except for the use of a cleansing type of nonreactive environment employed during the secondary recrystallization treatment. Several variations of processing from the 0.1 inch intermediate to the final thickness may be employed. For instance, the annealed intermediate may be cold rolled in 50 percent stages using intermediate anneals at temperatures ranging from about 700 C. to 900 C. for five minutes or the material may be rolled in percent stages with minute intermediate anneals at 900 C. until a thickness of 0.03 inch is reached. The material may then be annealed between 900 C. and 1000 C. for from 30 minutes tofour hours and then cold rolled to 0.012 inch. Cold reduction between anneals should not exceed about 70 percent. The secondary recrystallization is completed through both the first and second stage in a cleansing environment to produce the cubeon-edge type texture. The term oube-on-edge as used herein is meant to include grains wherein the (110) planes are within 5 to 10 parallel to the rolling plane.

The following example illustrates one method which may be employed to produce this texture:

EXAMPLE 4 The 0.1 inch intermediate, annealed as in the previous examples, was cold rolled in stages of about 50 percent to a strip thickness of 0.006 inch, the material being annealed between reduction stages at 900 C. for 30 minutes in dry hydrogen.

The strip was electropolished and then heated in a vacuum (about 5 X 10 mm. of mercury) ata temperature of about 1200 C. for three hours to insure completion of the second stage of secondary recrystallization. After the anneal, the strip consisted entirely of large grains having the (110) [001] orientation and exhibited electrically-determined torque values of the order of about 120,000 ergs./ cc. (about 80 percent texture) and peak ratios of about 0.35. Similar results were obtained using hydrogen of not higher than -40 F. dew point as the cleansing environment.

To produce thin tapes having the cube-on-edge orientation and which have a high residual-to-saturation induction, an annealed 0.100 inch thick intermediate produced by the process already outlined is cold rolled in cold reduction stages ranging from 40 to 70 percent reduction per pass :to a final thickness of up to 3 mils. Between successive cold rolling stages, the material is subjected to intermediate anneals to recrystallize the material at temperatures ranging from 700 C. to 1200 C. in a dry hydrogen atmosphere. The final step in the development of thin tape material having the cube-on-edge or (110) [001] orientation is a final texture-developing anneal which is carried out at a temperature of from 1000 C. to 1350 C. for times sufficient to develop the texture, for example, from 0.1 to about 10 hours, depending upon the temperature used. The atmosphere during the final anneal is vacuum, presusres not greater than about 4X10" mm. of mercury being preferred to develop the required orientation. Lower pressures can be used if desired.

If it is desired to treat long lengths of the tape, for example, the approximate 70-foot lengths that would be necessary to make a standard core of material 0.001 inch thick for use in electrical or electronic equipment, the tape can be subjected to a continuous anneal. During the continuous anneal, the tape travels through the annealing furnace at a rate which depends on furnace temperature and length of hot zone. a

Following all of the previously-described treatment, the thin tape then has the cube-on-edge orientation and is extremely well adapted for use in the construction of magnetic cores for use in eletcrical and electronic equipment. Prior to this invention, the best silicon cores produced had A.-C. residual-to-saturation induction ratios of only about 0.7. By contrast, cores constructed of the present material have A.-C. residual-to-saturation induc tions as high as 0.98. The cores are formed by first coating the tapes with a layer of magnesia to prevent sticking during subsequent annealing and then wound into toroids.

Once the toroids are formed, a stress relief anneal iseffected at from 900 C. to ,1 C. for periods of time suflicient to completely stress-relieve the metal. .Gen'- erally, annealing times of from 1 to 5 hours are suifiprepared by hot rolling high-purity ingots to an intermediate thickness of inch and then grinding the surface of the intermediate stock to remove any oxidized material. Removal of the oxidized material at this stage is felt to be important since the amount of oxygen present at the surface of the body is believed to have an effect on the orientation which can ultimately be developed.

Upon removal of the oxidized material from the intermediate stock, the stock was annealed for one hour at 1000 C. in dry hydrogen having a dew point of --60 F. The slab was then cold rolled to 0.100 inches and annealed for 5 hours at 700 C. in hydrogen also having adew point of 60 F. The 0.100 inch material was subsequently cold rolled to 0.001 inch thick (1 mil) in stages of 50 percent cold reduction with hour intermediate anneals in dry hydrogen at 900 C. The resulting strips were slit to /2 inch widths, cleaned with acetone, and given a final anneal by passing the tape continuously through a furnace operating at 1175 to 1250 C. to produce a strong [001] texture by secondary recrystallization. The rate of travel was 9 inches per hour and the annealing atmosphere !was vacuum, the pressure being 4X10 mm. of mercury.

After the anneal, the tapes were coated with an alcohol slurry of MgO, wound into a toroid of 44 turns and given a stress relief anneal at 900 C. for 5 hours in dry hydrogen.

The cores wound of this material were then tested for both D.-C. and A.-C. properties and it was found that these properties were surprisingly much better than had previously ever been obtained from silicon-iron alloys having similar silicon contents. The D.-C. properties for one of the coilstested are shown in Table I below:

Similarly, the A.-C. properties or" the same specimen Were measured and the watt losses and excitations measured at .difierent induction levels and for different fre quencies. These results are shown in Table II:

Table II A.'C. PROPERTIES [Losses-watts/lb. Indnctionkilgausses]' By comparing the properties of toroids made of the material of the present invention with the properties of toroids made from prior art silicon-iron alloys, it can readily be seen that the properties of the former are markedly superior. For example, toroids made from commerciflly available silicon-irons have coercive forces norm-ally not less than about 0.250 oersted, whereas the present material was measured at 0.125. Similarly, the residual induction of the present material was measured at 16,150 gausses, wherea the prior art material normally could not exceed approximately 13,000 to 13,500 gausses. It is also important to note that the novel bodies have a high residual-to-saturation induction ratio, values of from 0.84 to 0.90 being obtained from D.-C'. measurements. Ratios of residual-to-saturation induction from A.-C. measurements are from 0.91 to 0.98. Here, once again, the properties obtained know no equiv. alent in prior art silicon-iron alloys.

It is thus apparent that the present invention provides magnetic bodies having markedly superior properties to those which have been obtainable in the past.

Although the present invention has been described in connection with preferred embodiments, it is to be understood that modifications =and variations may be resorted 5 to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims. 7 p 50 What I claim as new and desire to secure'by Letters Patent of the United States is:

1. The method of producing a body consisting essentially of 2 to 6 weight percent silicon, not more than about 0.2 weight percent incidental impurities, remainder substantially all iron and having a majorityof the grains in a preferred crystalline orientation selected from the group consisting of (ll0)[001] and (100) [001] comprising, forming a body of the alloy up to about mils thickness which contains .not more than about 0.005 weight percent oxygen, annealing the body art a temperature of from about 1000" C. to about 1350 C. in a selected environment from the group consisting of krypton, argon, hydrogen and vacuum for a period of time controlling the amount of oxygen present at the surface of the body to not more than about 6 p.p.rn. to obtain the (110)[001] orientation and in excess of about 6 ppm. up to about ppm. to obtain the (100) [001] crystalline orientation. q

2. A method as defined in claim-1 wherein said environment is argon.

3. A method as defined in claim 1 wherein said environment is hydrogen.

4. A method as defined in claim 1 wherein said environment is vacuum.

5. The method of producing a body consisting essentially of 2 to 6 weight percent silicon, not more than about 0.2 weight percent incidental impurities, remainder substantially all iron and having a majority of the grains in the [001] crystalline orientation comprising, forming a body of the alloy of not more than about 15 mils thickness which contains not more than about 0.005 weight percent oxygen, annealing the body at a temperature of from about 1000 C. to about 1350 C. in an argon environment regulating the amount of oxygen present at the surface of the body to not less than about 6 ppm. up to about 50 p.p.m. thereby causing a majority of the grains in the body to assume the (100) [001] crystalline orientation.

6. The method of producing a body consisting essentially of 2 to 6 weight percent silicon, not more than about 0.2 weight percent incidental impurities, remainder substantially all iron and having a majority of the grains in the (1l0)[00'1] crystalline orientation comprising, forming a body of the alloy of not more than about 15 mils thickness which contains not more than about 0005 Weight percent oxygen, reducing the oxygen content at the surface of the body to not more than about 6- p.p.m., annealing the body at a temperature of from about 1000 C. to about 1350 C. in an oxygen-free argon atmosphere for a period of time causing a majority of the grains in the body to assume the [001] crystalline orientation.

7. The method of producing a body consisting essentially of 2 to 6 weight percent silicon, not more than about 0.2 weight percent incidental impurities, remainder substantially all iron and havinga majority of the grains in a preferred crystalline orientation selected ifrom the group consisting of (110) [001] and (100) [001] comprising, forming a body of the alloy of not more than about .15 mils thickness-which contains not more than about 0.005 weight percent oxygen, annealing the body at a temperature offrom about 1000 C. to about 1350"v C. in a selected environment to regulate the oxygen content of said body to not more than 6 p.p.m. to obtain (110) [001]crystalline orientation and to regulate the oxygen content of said body to be in excess of 6 ppm. to produce 100) [0011crystalline orientation.

8. The method of producing a grain oriented alloy body having a majority of the grains in the cube-onedge texture crystalline orientation comprising, preparing an alloy body of up to 15 mils thickness containing from 2 to 6 weight percent silicon, not more than about 0.2 weight pecent impurities including not more than about 0.005 weight percent oxygen, remainder substantially all iron, annealing said body at a temperature or from about 1000 C. to about 1350" C., and subjecting said body to a cleansing environment during annealing for a time sufiicient to lower the oxygen content of the alloy body tornot more than about 6 ppm.

9. The method of producing a grain oriented alloy body having a majority of the grains in the cube texture crystalline orientation comprising, preparing an alloy body of up to about 15 mils thickness containing from 2 to 6 =weight percent silicon, not more than about 0.2 weight percent impurities including not more than about 0.005 weight percent oxygen, remainder substantially all iron, annealing said body at a temperature of from about 1000 C. to about 1350 C., and subjecting said body to an argon environment during annealing to maintain the. oxygen content at the surface of the alloy body in excess of about 6 ppm. up to about 50 ppm.

, 10. The process as defined in. claim 8 wherein said cleansing environment is vacuum containing no more than about 1 micron of oxygen.

11. Theprocess as defined in claim 8 wherein said cleansing environment is hydrogen having a dew point no higher than about 40 F.

12. The method of producing the body of an alloy consisting of 2 to 6 weight percent silicon, not more than about 0.2 weight percent incidental impurities including not more than about 0005 Weight percent oxygen, remainder substantially all iron and having a majority of the grains in a preferred crystalline orientation selected from the group consisting of (110) [001] and (100) [001] comprising, providing a cast body of said alloy having randomly oriented grains, reducing the thickness of said body forming an intermediate sheet metal product in which a substantial portion of the reduction is effected through hot Working in substantially one direction, annealing said product at an elevated temperature, cold rolling said annealed intermediate at least 25 percent in substantially the same direction using intermediate anneals Where required in producing a rolled body of up to about 15 mils thickness, annealing the final product at a temperature of from about 100 C. to about 1350 C. in a selected environment for a period of time controlling the amount of oxygen present at the surface of the body to not more than about 6 ppm. to obtain the (110) [001] orientation and in excess of about 6 ppm. up to about 50 p.p.m. to obtain the (100) [001] crystalline orientation.

13. The method of producing the body of an alloy consisting essentially .of 2 to 6 Weight percent silicon, not more than about 0.2 weight percent incidental impurities including not more than about 0.005 weight percent oxygen, remainder substantially all iron and having a majority of the grains in a preferred crystalline orientation selected from the group consisting of'(1l0) [001] and (100) [001] comprising, providing a cast body of said alloy having randomly oriented grains, reducing the thickness of said body forming an intermediate sheet metal product in which a substantial portion of the reduction is effected through hot Working in substantially one direction, annealing said product at an elevated temperature, cold rolling said anealed intermediate to a reduction within the range of about 40.0 percent to 99.5 percent in substantially the same direction, using intermediate anneals Where required in producing a rolled body of up to about 15 mils in thickness, annealing the final product at a temperature of from about 1000 C. to about 1350 C. in a selected environment for a period of time controlling the amount of oxygen present at the surface of the body to not more than about 6 ppm. to obtain the (110) [001] orientation and in excess of 6 ppm. up to about 50 ppm. to obtain the (1 [0001] crystalline orientation.

14. A method of producing a thin section of a substantially pure iron-silicon alloy characterized by a bodycentered cubic lattice in which a majority of the grains have a cube-on-face texture in which the [001] directions are oriented 20 to 30 on either side of the rolling direction comprising, providing a cast body of said alloy containing about 2 to 6 Weight percent silicon, not more than about 0.2 weight percent incidental impurities, in cluding not more than about 0.005 Weight percent oxygen, remainder substantially all iron and having 'random ly oriented grains, reducing the thickness of said body to form an intermediate sheet metal product in which a substantial portion of the reduction is effected through hot working in substantially one direction, annealing said intermediate at an elevated temperature, cold rolling said intermediate to a reduction of about 70.0 percent to 99.5 percent in substantially the same direction, using intermediate anneals where more than one cold rolling reduction is used in producing a final product of thickness not exceeding about mils, said final product having been arrived at by cold reducing over the range of 70.0 percent to 99.5 percent following the intermediate anneal, annealing said final product at an elevated temperature 1 a 1cted nonreactive atmosphere for a time sulfi- .16 cient to effect a first-stage secondary recrystallization of said product into said aforementioned preferred orientation.

15. A method of producing a thin section of a substantially pure iron-silicon alloy characterized by a bodycentered cubic lattice in which a majority of the grains have a cube-on-face type texture in which the [001] directions are random with respect to the rolling directions comprising, providing a cast body of said alloy containing about 2 to '6- Weight percent silicon,'not more than about 0.2 Weight percent incidental impurities, in-

eluding not more than about 0.005 weight percent oxygen, and having randomly oriented grains, reducing the thickness of said body to form an intermediate sheet metal product in which a substantial portion of the reduction is effected through hot Working in substantially one direction, annealing said intermediate at an elevated temperature, cold rolling said intermediate to, a reduction of about 70 percent to percent in substantially the same direction, annealing said cold rolled material at an elevated temperature for a time sufficient to effect primary recrystallization and further cold rolling said material about 40 percent to 70 percent to a thickness not exceeding about 15 mils, annealing said finally rolled product at an elevated temperature in a selected nonreactive atmosphere for a time sulficient to effect a first. stage secondary recrystallization of said product into said aforementioned preferred orientation.

16. A method of producing a thin section of a substantially pure iron-silicon alloy characterized by a bodycentered cubic lattice in which a majority of the grains have a cube-on-face orientation in which the [001] directions are oriented within 10 of parallel to'the rolling direction comprising, providing a cast body of said alloy containing about 2 to 6 weight percent silicon, not more than about 0.2 weight percent incidental impurities,' ineluding not more than about 0005 Weight percent oxygen, and having randomly oriented grains, reducing the thickness of said body to form an intermediate sheet metal product in which a substantial portion of the reduction is effected through hot Working in substantially one direction, annealing said intermediate product at an elevated temperature, cold rolling said intermediate at reduction stages of about 25 percent to 70 percent in substantially the same direction, each reduction stage being separated by an intermediate anneal until a thickness not exceeding about 15 mils has been reached, annealing said finally rolled product at an elevated temperature in a selected nonreactive atmosphere for a time sufficient to effect a first-stage secondary recrystallization of said prodnot into said aforementioned preferred orientation.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Bozorth: Ferromagnetism, p. 85, 1951, by Van NostrandCo, "Inc, Lib., call No. 00 753, 136*. I. of Applied Physics, article by Kohler, supplement to vol. 31, No. 5, May 1960, pp. 4088-4095, 

1. THE METHOD OF PRODUCING A BODY CONSISTING ESSENTIALLY OF 7 TO 6 WEIGHT PERCENT SILICON, NOT MORE THAN ABOOUT 0.2 WEIGHT PERCENT INCIDENTAL IMPURITIES, REMAINDER SUBSTANTIALLY ALL IRON AND HAVING A MAJORITY OF THE GRAINS IN A PREFERRED CRYSTALLINE ORIENTATION SELECTED FROM THE GROUP CONSISTING OF (110( 001! AND (100( 001! COMPRISING, FORMING A BODY OF THE ALLOY UP TO ABOUT 15 MILS THICKNESS WHICH CONTAINS NOT MORE THAN ABOUT 0.005 WEIGHT PERCENT OXYGEN, ANNEALING THE BODY AT A TEMPERATURE OF FROM ABOUT 1000*C. TO ABOUT 1350*C. IN A SELECTED ENVIRONMENT FROM THE GROUP CONSISTING OF KRYPTON, ARGON, HYDROGEN AND VACUUM FOR A PERIOD OF TIME CONTROLLING THE AMOUNT OF OXYGEN PRESENT AT THE SURFACE OF THE BODY TO NOT MORE THAN ABOUT 6 P.P.M. TO OBTAIN THE (110) 001! ORIENTATION AND IN EXCESS OF ABOUT 6 P.P.M. UP TO ABOUT 50 P.P.M. TO OBTAIN THE (110) 001! CRYSTALLINE ORIENTATION. 